The latest comes from CNN/ORC International, which released a poll Monday showing Mr. Christie trailing by 16 percentage points, with 39% of the vote, compared with Mrs. Clinton’s 55%. Prior to January’s “bridgegate” scandal, Mr. Christie led the former secretary of state by two percentage points—48%-46%—and topped the list of possible Republican contenders in the presidential race, according to a December CNN/ORC poll.

The new survey was taken Jan. 31 through Feb. 2, just as a lawyer for a Port Authority official involved in the lane closures at the George Washington Bridge asserted that evidence existed showing Mr. Christie knew of the traffic mess while it was taking place. Last month, Mr. Christie denied any knowledge of the lane closures in a two-hour press conference, and he has denied the official’s allegations.

A Washington Post/ABC News poll released last week showed Mr. Christie in third place for the Republican nomination, behind Rep. Paul Ryan (R., Wis.) and former Florida Gov. Jeb Bush. The poll also showed Mrs. Clinton leading Mr. Christie by 12 percentage points, 53%-41%.